1. Field of the Invention
The present invention relates to a QFN package and manufacturing process thereof, and more particularly, to a QFN package with composite bumps.
2. Descriptions of the Related Art
Semiconductor packaging processes have been widely used to electrically connect a semiconductor chip to an external component with a better reliability and also to protect the semiconductor chip from damages caused by external conditions. However, packaging materials and the packaging processes used are not only associated with the manufacturing cost, but also have an influence on operational performance of the packaged chip. For this reason, the packaging structure and materials thereof selected for use become very important.
Among several package technologies, Quad Flat No-Leaded (QFN) semiconductor packages have achieved wide popularity in recent years because of their smaller package size. In a conventional QFN semiconductor package, a chip is electrically connected to a lead frame by wire, with each bond pad of the chip being electrically connected to a corresponding lead of the lead frame respectively. As to a flip chip QFN package 10, a chip 101 is electrically connected to a lead frame 103 by bumps 105 as shown in FIG. 1A or FIG. 1C. The chip 101 is flipped and bonded on the lead frame 103 by solder joining of solder bump (FIG. 1A) or copper pillar with solder cap. Due to reflow for melting the solder bump or solder cap on copper pillar to solder join the bump 105 of chip 101 and lead of lead frame 103, the lead width will be limited to enough space for avoid the melting solder over flow to the opposite side of lead during the reflow process (FIG. 1B). That melting solder 107 over flow on the opposite side of lead will induce assembly defect of further process, for example encapsulation, or SMT (Surface Mount Technology).
Unfortunately, sometimes limitation of chip size and package size, the lead width may not be designed with enough space to avoid the melting solder over flow. In view of this, it is highly desirable in the art to provide a solution that can improve the limitation of lead width and also provide a lower the manufacturing cost of a packaging structure.